Ueda san, ok, I see now. Thank you.

It is my pleasure. As for your question, you are absolutely right. You could just say "何時から(ですか) " depending on the context. I would, however, add "朝" at the beginning of the sentence and say "朝何時から(ですか) " so as to make it clearer that I am asking about their opening hour.

Ueda san, thank you for all your corrections. I can't understand one moment: when I talk about a time of starting of my workday, can't I jut say "from what time" - "何時から" considering that both me and the listener understand that speech is about my workday? Because, If I understand correctly, when I need to ask, for example, what time does some organization, (e.g. bank), open, I ask simply "何時 からですか?" Or I get something wrong?

うちへ 何時（何時→何時に）〔何時にうちへ would be more natural.〕 帰りますか? ／6時半に 帰ります。／毎日ですか?　／はい、そ（そ→そう）です。／大変ですね。

何時 から（何時から→何時から仕事）ですか?〔I guess you mean at what time do you start working.〕／8時に から（にから→から）です。／なんで行きますか?　／歩いて 行きます。